Conventional sheet-fed, offset rotary printing presses typically include one or more printing stations through which individual sheets are fed and printed with wet ink. After final printing, the sheets are fed by a delivery conveyor system to the delivery end of the press where the freshly printed sheets are collected and stacked. In a typical sheet-fed, offset rotary printing press such as the Heidelberg Speedmaster line of presses, the delivery conveyor system includes a pair of endless gripper chains carrying spaced laterally disposed gripper bars and grippers which are used to grip and pull freshly printed sheets from the impression cylinder and convey the sheets toward the sheet delivery stacker. The gripper chains are driven in precisely timed relation to the impression cylinder by gripper chain sprocket wheels which are laterally spaced between a delivery drive shaft mounted on opposite sides of the press frame. The delivery drive shaft is mechanically coupled by gears for synchronous rotation with the impression cylinder.
Since the inks used with offset type printing presses typically remain wet and tacky for some time after printing, special precautions must be taken to insure that the wet inked surface of the freshly printed sheets is not marked or smeared as the sheets are transferred from one printing station to another, and through the delivery system to the sheet delivery stacker. The printed surface of the paper dries relatively slowly and can be smeared during subsequent processing, particularly when the printed sheets are stacked. In order to minimize smearing, a dryer may be mounted along the delivery path of the printed sheets, or an anti-offset spray powder may be sprayed on the printed surface.
In some printing applications, it is desirable that the press be capable of applying a protective and/or decorative coating over all or a portion of the surface of the printed sheets. Typical coating solutions include varnish, lacquer, dye, moisturizers and ink. Such coatings typically are formed of a UV-curable or water-soluble resin applied as a liquid solution or emulsion by an applicator roller over the freshly printed sheets to protect the ink and improve the appearance of the sheets. Use of such coatings is particularly desirable when decorative or protective finishes are required such as in the production of posters, record jackets, brochures, magazines, folding cartons and the like. In cases where a liquid coating is to be applied, the coating operation is carried out after the final ink printing has been performed, most desirably by an in-line coating application.